Did it ever occur to you that out of all the people you could have had for a roommate, God gave you this person? He has a reason for bringing you together, and I believe He wants to use you to help your roommate understand who Christ is and what He can do in her life.
Ask God, therefore, to help you be a living demonstration of Christ's love to her. Begin by being the best friend you can possibly be. It probably hasn't been easy for your roommate to adjust to life in this country (especially on a college campus); she may even wonder if she's made the right decision by coming here. (You'd probably feel the same way if you were studying in her country.) Let her know you care about her and want to help her in every way you can. The Bible says, "May the Lord make your love increase and overflow for each other and for everyone else" (1 Thessalonians 3:12).
Then ask God to help her see what difference Christ makes in your life. Most of the people she'll meet may not believe in Christ or seek to follow Him, but if you are a Christian, you're called to be different. Jesus said, "Let your light so shine before men, that they may see your good works and praise your Father in heaven" (Matthew 5:16).
Most of all, pray for your roommate, and ask God to help you share Christ with her. God loves her and has a plan for her life -- just as He does for you.